SCHED_FIFO线程被Linux中的SCHED_OTHER线程抢占

/* Includes */
#include <unistd.h>     /* Symbolic Constants */
#include <sys/types.h>  /* Primitive System Data Types */ 
#include <errno.h>      /* Errors */
#include <stdio.h>      /* Input/Output */
#include <stdlib.h>     /* General Utilities */
#include <pthread.h>    /* POSIX Threads */
#include <string.h>     /* String handling */
#include <sched.h>
/* prototype for thread routine */
void print_message_function ( void *ptr );
void print_message_function1 ( void *ptr );

/* struct to hold data to be passed to a thread
this shows how multiple data items can be passed to a thread */
typedef struct str_thdata
{
int thread_no;
int thread_value;
char message[100];
  } thdata;

int main()
  {
pthread_t thread1,thread2;  /* thread variables */
thdata data1,data2;         /* structs to be passed to threads */

/* initialize data to pass to thread 1 */
data1.thread_no = 1;
data1.thread_value = 0;
strcpy(data1.message,"Hello!");

/* initialize data to pass to thread 2 */
data2.thread_no = 2;
data2.thread_value = 10000;
strcpy(data2.message,"Hi!");

/* create threads 1 and 2 */    
pthread_create (&thread1,NULL,(void *) &print_message_function,(void *) &data1);
pthread_create (&thread2,(void *) &print_message_function1,(void *) &data2);

/* Main block now waits for both threads to terminate,before it exits
   If main block exits,both threads exit,even if the threads have not
   finished their work */ 
pthread_join(thread1,NULL);
pthread_join(thread2,NULL);

/* exit */  
exit(0);
} /* main() */

/** 
* print_message_function is used as the start routine for the threads used
* it accepts a void pointer 
**/
void print_message_function ( void *ptr )
{

thdata *data;            
data = (thdata *) ptr;  /* type cast to a pointer to thdata */

struct sched_param param;
//int priority=10;
/* sched_priority will be the priority of the thread */
//param.sched_priority = priority;
/* only supported policy,others will result in ENOTSUP */

int policy = SCHED_OTHER;
/* scheduling parameters of target thread */
pthread_setschedparam(pthread_self(),policy,&param);
printf("Thread %d says sched policy  %d n",data->thread_no,SCHED_OTHER);
pthread_getschedparam(pthread_self(),&policy,&param);

printf("Thread %d says %s  %d n",data->message,policy);

int i=0;
/* do the work */
printf("Thread %d says %s %d n",(int)pthread_self());
for(i=0;i<100;i++)

printf("Thread %d says %d n",data->thread_value++);
pthread_exit(0); /* exit */
} /* print_message_function ( void *ptr ) */



void print_message_function1 ( void *ptr )
{

thdata *data;            
data = (thdata *) ptr;  /* type cast to a pointer to thdata */

struct sched_param param;
int priority=10;
/* sched_priority will be the priority of the thread */
param.sched_priority = priority;
/* only supported policy,others will result in ENOTSUP * /

int policy = SCHED_FIFO;
/* scheduling parameters of target thread */
pthread_setschedparam(pthread_self(),&param);
printf("Thread %d says sched policy %d n",SCHED_FIFO);

pthread_getschedparam(pthread_self(),policy);

int i=0;
/* do the work */
printf("Thread %d says %s  %d n",data->thread_value++);
pthread_exit(0); /* exit */
} /* print_message_function ( void *ptr ) */

我在多次运行中得到了意想不到的结果,我看到SCHED_FIFO被SCHED_OTHER线程抢占,即按程序,线程2处于FIFO模式,而线程1处于SCHED_OTHER模式.我已经多次看到thread2被thread1抢占了.

有人可以帮助我找到问题吗？